1. Field of the Invention
The present invention relates to the control of internal combustion engines and more particularly to a control method for an internal combustion engine equipped with an electronically controlled fuel injection system, which controls a quantity of fuel injected during a transitional period and an apparatus for performing that method.
2. Description of the Prior Art
In the past, it has been recognized that a quantity of fuel required for an engine during a transitional period differs from that required during a steady-state operation. Thus, with an engine equipped for example with a speed-density type electronic fuel injection system, a quantity of fuel injected during a transitional period is controlled by obtaining a quantity of change of an intake pipe pressure or a throttle position at intervals of a given time period so that when its value is greater than a predetermined value, a fuel injection quantity correction factor predetermined with respect to an engine cooling water temperature or with respect to a cooling water temperature and an amount of change of controlling factors is obtained and a basic fuel injection quantity determined by an engine speed and an intake pipe pressure is corrected in accordance with the value of a correction factor. Since this prior art method of controlling a fuel injection quantity during a transitional period computes an amount of change by sampling the controlling factors at intervals of a given time period for obtaining an amount of change of the controlling factors, a desired correction factor for correcting a basic fuel injection quantity is obtained in accordance with the amount of change of the controlling factors which is delayed in time as compared with the amount of change of controlling factors obtained by continuously sampling the controlling factors or the actual amount of change of the controlling factors. As a result, the correction of the fuel quantity cannot follow up or respond to the change of the actual air flow to the engine cylinders and thus the air-fuel ratio within the cylinders becomes lean causing the engine to backfire or become unsteady during the transitional period, particularly at a low temperature of the engine cooling water.